Technical Field
The present invention relates to a metal oxide supported palladium catalyst, the preparation thereof, and its use for the oxidation of hydrocarbon compounds. More specifically, the present invention relates to a β-Bi2O3/Bi2Sn2O7 hetero-junction supported palladium catalyst for fluorene oxidation under ultraviolet irradiation.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Aromatic hydrocarbons, especially polycyclic aromatic hydrocarbons (PAHs) and other organic compounds found in association with PAHs, are potent carcinogens and teratogens for a variety of organisms. Many of these chemicals are implicated in serious human disease states such as respiratory diseases and cancer [D. B. Kittelson, J. Aerosol Sci. 29 (1998) 575-588—incorporated herein by reference in its entirety]. PAHs currently represent the most abundant man-made pollutant on earth. These chemicals possess relatively long residence times and can enter into the atmosphere, rivers and soil through a variety of means including evaporation, diffusion and permeation. Fluorene, one such polycyclic aromatic hydrocarbon (PAH), is formed during the combustion of fossil fuels, incomplete fuel combustion [O. Gimeno, F. J. Rivas, F. J. Beltran, M. Carbajo, Chemosphere 69 (2007) 595-604—incorporated herein by reference in its entirety], asphalt production [J. P. Buchet, J. P. Gennart, F. Mercado-Calderon, J. P. Delavignette, L. Cupers, R. Lauwerys, Br J Ind Med 49 (1992) 761-768—incorporated herein by reference in its entirety] and automotive exhaust emissions [M. Baerns, H. Borchert, R. Kalthoff, P. KaDner, F. Majunke, S. Trautmann, A. Zein, P. Ruiz and B. Delmon (Eds.) Catalysis Studies in Surface Science and Catalysis, Vol. 12, pp. 51-60; J. Bünger, J. Krahl, A. Weigel, O. Schröder, T. Brüning, M. Müller, E. Hallier, G. Wesphal, Arch. Toxicol. 80 (2006) 540-546; J. Sabate, J. M. Bayona, A. M. Solanas, Chemosphere 44 (2001) 119-124—each incorporated herein by reference in its entirety]. Like many PAHs, fluorene is reported to possess potent mutagenic and carcinogenic properties [H. T. Yu, J Environ Sci. Health Part C: Environ Carcinog & Ecotoxicol Rev. 20 (2002) 149-83; Y. C. Lin, W. J. Lee, H. C. Hou, Atmos. Environ. 40 (2006) 3930-3940—each incorporated herein by reference in its entirety].
Owing to their toxicity, the degradation and removal of PAHs has been the focus of numerous studies [L. Liu, B. Yang, H. Zhang, S. Tang, Z. Xie, H. Wang, Z. Wang, P. Lu, Y. Ma, J. Phys. Chem. C, 112 (2008) 10273-10278—incorporated herein by reference in its entirety]. Photocatalytic oxidation is one strategy used for the degradation of PAHs [M. M. Mohamed, S. A. Ahmed, K. S. Khairou, Appl. Catal. B: Environ. 150-151 (2014) 63-73—incorporated herein by reference in its entirety], which involves the use of visible light irradiation in lieu of high temperatures and/or harsh/toxic oxidants that are commonplace in traditional oxidative catalysis [N. T. Vandenborre, E. Husson, H. Brusset, Spectrochim. Acta A 37 (1981) 113—incorporated herein by reference in its entirety]. While complete oxidation without a photocatalyst is thermodynamically possible, this process is kinetically slow and is therefore not ideal. The removal of fluorene, through oxidative degradation pathways to furnish fluorenol/fluorenone products, has only been accomplished on small scale and through the use of harsh oxidants [S. M. Correa, G. Arbilla, Atmos. Environ. 40 (2006) 6821-6826—incorporated herein by reference in its entirety]. A benefit of pursuing such fluorene oxidative removal strategies is that the fluorenone/fluorenol products can be utilized as building blocks for the synthesis of antimalarial drugs, insecticides, algaecides, biopharmaceutical dyes and optical brightening agents [D. Dunn, G. Hostetler, M. Iqbal, V. R. Marcy, Y. G. Lin, B. Jones, L. D. Aimone, J. Gruner, M. A. Ator, E. R. Bacon, S. Chatterjee, Bioorganic & Medicinal Chemistry Letters 22 (11) (2012) 3751-3753—incorporated herein by reference in its entirety]. In addition, their light and temperature sensitivities, heat resistance, conductivity and corrosion resistance make fluorenol/fluorenone useful materials in the areas of thermo and light sensitization, luminescence chemistry, spectrophotometric analysis and molecular chemistry [T. A. M. Ferenczi, M. Sims and D. D. C. Bradley J. Phys.: Condens. Matter 20(4) (2008) 045220-045224; L. Feng, C. Zhang, H. Bie, Z. Chen, Dyes & Pigments 64 (2005) 31-40—incorporated herein by reference in its entirety].
The most common photocatalytic oxidative systems generally include one or more ultraviolet (UV) energy sources for irradiating UV light onto an organic substrate in the presence of a photocatalyst. Titanium dioxide (TiO2) remains the most popular and most prevalent photocatalyst because it is a light, strong, anti-corrosive, and inexpensive material. When excited by radiation with a wavelength less than 400 nm (radiation in the near-UV range), titanium dioxide photocatalysts generate electron/hole pairs (h+), which act as strong oxidizing agents to adsorbed species. In the presence of molecular oxygen and/or water, these electron/hole pairs can lead to superoxide (O2—.) or hydroxyl radicals (OH.), which can then in turn oxidize and degrade organic matter.
Although the use of titanium dioxide as a photocatalyst has been widespread, other photocatalysts have also used been used including: stannic oxide, zinc oxide, vanadium oxide, dibismuth trioxide, tungsten trioxide, ferric oxide, zirconium oxide, antimony oxide, and cerium oxide (K. Garfield, J. Potter, U.S. Pat. No. 7,820,100 B2—incorporated herein by reference in its entirety). As is the case with these materials, many photocatalytic systems involve the use of one metal or metal oxide. The use of multiple metals and/or metal oxides for photocatalytic oxidation is less explored. Bismuth oxide (Bi2O3) is an attractive material for oxidative photocatalysis because of its good electrical conductivity and thermal properties. It is extensively used in various applications such as microelectronics, sensor technology and optical coatings [W. D. He, W. Qin, X. H. Wu, X. B. Ding, L. Chen, Z. H. Jiang, Thin Solid Films 515 (2007) 5362-5365; S. J. A. Moniz, D. Bhachu, C. S. Blackman, A. J. Cross, S. Elouali, D. Pugh, R. Q. Cabrera, S. Vallejos, Inorg. Chim. Acta 380 (2012) 328-335—each incorporated herein by reference in its entirety]. As a photocatalyst, Bi2O3 is a p-type semiconductor with conduction and valence band edges +0.33 and +3.13 V relative to Normal hydrogen electrode (NHE), respectively. These values account for its capability to oxidize water and possibly generate highly reactive species, such as O2—. and OH. radicals, which may act as initiators for oxidation reactions. On the other hand, SnO2 is an important n-type wide-band gap semiconductor with broad applications based on electrical and optical properties of the oxide, which can also be used as strong oxidation catalysts [N. Van Hieu, L. T. B. Thuy, N. D. Chien, Sensors and Actuators B 129 (2008) 888-895—incorporated herein by reference in its entirety].
There is ongoing research to identify new bismuth and tin oxide containing materials with unique properties for various applications, such as photocatalysis. Wang et al. (Chinese Patent No. CN101530797A—incorporated herein by reference in its entirety) disclosed a core-shell structured catalyst comprising a mixture of tin dioxide and bismuth oxide wherein a noble metal such as palladium (Pd) is distributed on the surface of the core material. This mixed oxide core-shell catalyst can be used for carbon monoxide oxidations, methanol and alcohol electro-oxidations, and oxygen electro-reduction chemistry.
Hiroshi et al. (Japanese Patent No. JP6040961B2—incorporated herein by reference in its entirety) disclosed the preparation of an alcohol/aldehyde oxidation catalyst by supporting palladium, bismuth, and tin on an inorganic support.
Kobayashi, H. (Japanese Patent No. JP04348351B2—incorporated herein by reference in its entirety) disclosed a photocatalyst containing palladium along with a mixture of bismuth oxide and tin oxide for use as a decomposition product oxidant.
In view of the forgoing, the objective of the present invention is to synthesize new and active catalysts comprised of multiple metals/metal oxides capable of converting fluorene to fluorenol/fluorenone using a mild oxidant and ultraviolet irradiation.